fs/notify/dnotify/dnotify.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Directory notifications for Linux.
   4  *
   5  * Copyright (C) 2000,2001,2002 Stephen Rothwell
   6  *
   7  * Copyright (C) 2009 Eric Paris <Red Hat Inc>
   8  * dnotify was largly rewritten to use the new fsnotify infrastructure
   9  */
  10 #include <linux/fs.h>
  11 #include <linux/module.h>
  12 #include <linux/sched.h>
  13 #include <linux/sched/signal.h>
  14 #include <linux/dnotify.h>
  15 #include <linux/init.h>
  16 #include <linux/spinlock.h>
  17 #include <linux/slab.h>
  18 #include <linux/fdtable.h>
  19 #include <linux/fsnotify_backend.h>
  20
  21 int dir_notify_enable __read_mostly = 1;
  22
  23 static struct kmem_cache *dnotify_struct_cache __read_mostly;
  24 static struct kmem_cache *dnotify_mark_cache __read_mostly;
  25 static struct fsnotify_group *dnotify_group __read_mostly;
  26
  27 /*
  28  * dnotify will attach one of these to each inode (i_fsnotify_marks) which
  29  * is being watched by dnotify.  If multiple userspace applications are watching
  30  * the same directory with dnotify their information is chained in dn
  31  */
  32 struct dnotify_mark {
  33         struct fsnotify_mark fsn_mark;
  34         struct dnotify_struct *dn;
  35 };
  36
  37 /*
  38  * When a process starts or stops watching an inode the set of events which
  39  * dnotify cares about for that inode may change.  This function runs the
  40  * list of everything receiving dnotify events about this directory and calculates
  41  * the set of all those events.  After it updates what dnotify is interested in
  42  * it calls the fsnotify function so it can update the set of all events relevant
  43  * to this inode.
  44  */
  45 static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
  46 {
  47         __u32 new_mask = 0;
  48         struct dnotify_struct *dn;
  49         struct dnotify_mark *dn_mark  = container_of(fsn_mark,
  50                                                      struct dnotify_mark,
  51                                                      fsn_mark);
  52
  53         assert_spin_locked(&fsn_mark->lock);
  54
  55         for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
  56                 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
  57         if (fsn_mark->mask == new_mask)
  58                 return;
  59         fsn_mark->mask = new_mask;
  60
  61         fsnotify_recalc_mask(fsn_mark->connector);
  62 }
  63
  64 /*
  65  * Mains fsnotify call where events are delivered to dnotify.
  66  * Find the dnotify mark on the relevant inode, run the list of dnotify structs
  67  * on that mark and determine which of them has expressed interest in receiving
  68  * events of this type.  When found send the correct process and signal and
  69  * destroy the dnotify struct if it was not registered to receive multiple
  70  * events.
  71  */
  72 static int dnotify_handle_event(struct fsnotify_group *group,
  73                                 struct inode *inode,
  74                                 u32 mask, const void *data, int data_type,
  75                                 const struct qstr *file_name, u32 cookie,
  76                                 struct fsnotify_iter_info *iter_info)
  77 {
  78         struct fsnotify_mark *inode_mark = fsnotify_iter_inode_mark(iter_info);
  79         struct dnotify_mark *dn_mark;
  80         struct dnotify_struct *dn;
  81         struct dnotify_struct **prev;
  82         struct fown_struct *fown;
  83         __u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
  84
  85         /* not a dir, dnotify doesn't care */
  86         if (!S_ISDIR(inode->i_mode))
  87                 return 0;
  88
  89         if (WARN_ON(fsnotify_iter_vfsmount_mark(iter_info)))
  90                 return 0;
  91
  92         dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
  93
  94         spin_lock(&inode_mark->lock);
  95         prev = &dn_mark->dn;
  96         while ((dn = *prev) != NULL) {
  97                 if ((dn->dn_mask & test_mask) == 0) {
  98                         prev = &dn->dn_next;
  99                         continue;
 100                 }
 101                 fown = &dn->dn_filp->f_owner;
 102                 send_sigio(fown, dn->dn_fd, POLL_MSG);
 103                 if (dn->dn_mask & FS_DN_MULTISHOT)
 104                         prev = &dn->dn_next;
 105                 else {
 106                         *prev = dn->dn_next;
 107                         kmem_cache_free(dnotify_struct_cache, dn);
 108                         dnotify_recalc_inode_mask(inode_mark);
 109                 }
 110         }
 111
 112         spin_unlock(&inode_mark->lock);
 113
 114         return 0;
 115 }
 116
 117 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
 118 {
 119         struct dnotify_mark *dn_mark = container_of(fsn_mark,
 120                                                     struct dnotify_mark,
 121                                                     fsn_mark);
 122
 123         BUG_ON(dn_mark->dn);
 124
 125         kmem_cache_free(dnotify_mark_cache, dn_mark);
 126 }
 127
 128 static const struct fsnotify_ops dnotify_fsnotify_ops = {
 129         .handle_event = dnotify_handle_event,
 130         .free_mark = dnotify_free_mark,
 131 };
 132
 133 /*
 134  * Called every time a file is closed.  Looks first for a dnotify mark on the
 135  * inode.  If one is found run all of the ->dn structures attached to that
 136  * mark for one relevant to this process closing the file and remove that
 137  * dnotify_struct.  If that was the last dnotify_struct also remove the
 138  * fsnotify_mark.
 139  */
 140 void dnotify_flush(struct file *filp, fl_owner_t id)
 141 {
 142         struct fsnotify_mark *fsn_mark;
 143         struct dnotify_mark *dn_mark;
 144         struct dnotify_struct *dn;
 145         struct dnotify_struct **prev;
 146         struct inode *inode;
 147         bool free = false;
 148
 149         inode = file_inode(filp);
 150         if (!S_ISDIR(inode->i_mode))
 151                 return;
 152
 153         fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
 154         if (!fsn_mark)
 155                 return;
 156         dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
 157
 158         mutex_lock(&dnotify_group->mark_mutex);
 159
 160         spin_lock(&fsn_mark->lock);
 161         prev = &dn_mark->dn;
 162         while ((dn = *prev) != NULL) {
 163                 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
 164                         *prev = dn->dn_next;
 165                         kmem_cache_free(dnotify_struct_cache, dn);
 166                         dnotify_recalc_inode_mask(fsn_mark);
 167                         break;
 168                 }
 169                 prev = &dn->dn_next;
 170         }
 171
 172         spin_unlock(&fsn_mark->lock);
 173
 174         /* nothing else could have found us thanks to the dnotify_groups
 175            mark_mutex */
 176         if (dn_mark->dn == NULL) {
 177                 fsnotify_detach_mark(fsn_mark);
 178                 free = true;
 179         }
 180
 181         mutex_unlock(&dnotify_group->mark_mutex);
 182
 183         if (free)
 184                 fsnotify_free_mark(fsn_mark);
 185         fsnotify_put_mark(fsn_mark);
 186 }
 187
 188 /* this conversion is done only at watch creation */
 189 static __u32 convert_arg(unsigned long arg)
 190 {
 191         __u32 new_mask = FS_EVENT_ON_CHILD;
 192
 193         if (arg & DN_MULTISHOT)
 194                 new_mask |= FS_DN_MULTISHOT;
 195         if (arg & DN_DELETE)
 196                 new_mask |= (FS_DELETE | FS_MOVED_FROM);
 197         if (arg & DN_MODIFY)
 198                 new_mask |= FS_MODIFY;
 199         if (arg & DN_ACCESS)
 200                 new_mask |= FS_ACCESS;
 201         if (arg & DN_ATTRIB)
 202                 new_mask |= FS_ATTRIB;
 203         if (arg & DN_RENAME)
 204                 new_mask |= FS_DN_RENAME;
 205         if (arg & DN_CREATE)
 206                 new_mask |= (FS_CREATE | FS_MOVED_TO);
 207
 208         return new_mask;
 209 }
 210
 211 /*
 212  * If multiple processes watch the same inode with dnotify there is only one
 213  * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
 214  * onto that mark.  This function either attaches the new dnotify_struct onto
 215  * that list, or it |= the mask onto an existing dnofiy_struct.
 216  */
 217 static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
 218                      fl_owner_t id, int fd, struct file *filp, __u32 mask)
 219 {
 220         struct dnotify_struct *odn;
 221
 222         odn = dn_mark->dn;
 223         while (odn != NULL) {
 224                 /* adding more events to existing dnofiy_struct? */
 225                 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
 226                         odn->dn_fd = fd;
 227                         odn->dn_mask |= mask;
 228                         return -EEXIST;
 229                 }
 230                 odn = odn->dn_next;
 231         }
 232
 233         dn->dn_mask = mask;
 234         dn->dn_fd = fd;
 235         dn->dn_filp = filp;
 236         dn->dn_owner = id;
 237         dn->dn_next = dn_mark->dn;
 238         dn_mark->dn = dn;
 239
 240         return 0;
 241 }
 242
 243 /*
 244  * When a process calls fcntl to attach a dnotify watch to a directory it ends
 245  * up here.  Allocate both a mark for fsnotify to add and a dnotify_struct to be
 246  * attached to the fsnotify_mark.
 247  */
 248 int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
 249 {
 250         struct dnotify_mark *new_dn_mark, *dn_mark;
 251         struct fsnotify_mark *new_fsn_mark, *fsn_mark;
 252         struct dnotify_struct *dn;
 253         struct inode *inode;
 254         fl_owner_t id = current->files;
 255         struct file *f;
 256         int destroy = 0, error = 0;
 257         __u32 mask;
 258
 259         /* we use these to tell if we need to kfree */
 260         new_fsn_mark = NULL;
 261         dn = NULL;
 262
 263         if (!dir_notify_enable) {
 264                 error = -EINVAL;
 265                 goto out_err;
 266         }
 267
 268         /* a 0 mask means we are explicitly removing the watch */
 269         if ((arg & ~DN_MULTISHOT) == 0) {
 270                 dnotify_flush(filp, id);
 271                 error = 0;
 272                 goto out_err;
 273         }
 274
 275         /* dnotify only works on directories */
 276         inode = file_inode(filp);
 277         if (!S_ISDIR(inode->i_mode)) {
 278                 error = -ENOTDIR;
 279                 goto out_err;
 280         }
 281
 282         /* expect most fcntl to add new rather than augment old */
 283         dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
 284         if (!dn) {
 285                 error = -ENOMEM;
 286                 goto out_err;
 287         }
 288
 289         /* new fsnotify mark, we expect most fcntl calls to add a new mark */
 290         new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
 291         if (!new_dn_mark) {
 292                 error = -ENOMEM;
 293                 goto out_err;
 294         }
 295
 296         /* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */
 297         mask = convert_arg(arg);
 298
 299         /* set up the new_fsn_mark and new_dn_mark */
 300         new_fsn_mark = &new_dn_mark->fsn_mark;
 301         fsnotify_init_mark(new_fsn_mark, dnotify_group);
 302         new_fsn_mark->mask = mask;
 303         new_dn_mark->dn = NULL;
 304
 305         /* this is needed to prevent the fcntl/close race described below */
 306         mutex_lock(&dnotify_group->mark_mutex);
 307
 308         /* add the new_fsn_mark or find an old one. */
 309         fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
 310         if (fsn_mark) {
 311                 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
 312                 spin_lock(&fsn_mark->lock);
 313         } else {
 314                 error = fsnotify_add_inode_mark_locked(new_fsn_mark, inode, 0);
 315                 if (error) {
 316                         mutex_unlock(&dnotify_group->mark_mutex);
 317                         goto out_err;
 318                 }
 319                 spin_lock(&new_fsn_mark->lock);
 320                 fsn_mark = new_fsn_mark;
 321                 dn_mark = new_dn_mark;
 322                 /* we used new_fsn_mark, so don't free it */
 323                 new_fsn_mark = NULL;
 324         }
 325
 326         rcu_read_lock();
 327         f = fcheck(fd);
 328         rcu_read_unlock();
 329
 330         /* if (f != filp) means that we lost a race and another task/thread
 331          * actually closed the fd we are still playing with before we grabbed
 332          * the dnotify_groups mark_mutex and fsn_mark->lock.  Since closing the
 333          * fd is the only time we clean up the marks we need to get our mark
 334          * off the list. */
 335         if (f != filp) {
 336                 /* if we added ourselves, shoot ourselves, it's possible that
 337                  * the flush actually did shoot this fsn_mark.  That's fine too
 338                  * since multiple calls to destroy_mark is perfectly safe, if
 339                  * we found a dn_mark already attached to the inode, just sod
 340                  * off silently as the flush at close time dealt with it.
 341                  */
 342                 if (dn_mark == new_dn_mark)
 343                         destroy = 1;
 344                 error = 0;
 345                 goto out;
 346         }
 347
 348         __f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);
 349
 350         error = attach_dn(dn, dn_mark, id, fd, filp, mask);
 351         /* !error means that we attached the dn to the dn_mark, so don't free it */
 352         if (!error)
 353                 dn = NULL;
 354         /* -EEXIST means that we didn't add this new dn and used an old one.
 355          * that isn't an error (and the unused dn should be freed) */
 356         else if (error == -EEXIST)
 357                 error = 0;
 358
 359         dnotify_recalc_inode_mask(fsn_mark);
 360 out:
 361         spin_unlock(&fsn_mark->lock);
 362
 363         if (destroy)
 364                 fsnotify_detach_mark(fsn_mark);
 365         mutex_unlock(&dnotify_group->mark_mutex);
 366         if (destroy)
 367                 fsnotify_free_mark(fsn_mark);
 368         fsnotify_put_mark(fsn_mark);
 369 out_err:
 370         if (new_fsn_mark)
 371                 fsnotify_put_mark(new_fsn_mark);
 372         if (dn)
 373                 kmem_cache_free(dnotify_struct_cache, dn);
 374         return error;
 375 }
 376
 377 static int __init dnotify_init(void)
 378 {
 379         dnotify_struct_cache = KMEM_CACHE(dnotify_struct,
 380                                           SLAB_PANIC|SLAB_ACCOUNT);
 381         dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
 382
 383         dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
 384         if (IS_ERR(dnotify_group))
 385                 panic("unable to allocate fsnotify group for dnotify\n");
 386         return 0;
 387 }
 388
 389 module_init(dnotify_init)